APCATA 417– 2012-190

IR study of iridium bonded to perturbed silanol groups of PtHZSM5
for npentane isomerization

The Ir/PtHZSM5
catalyst was prepared by impregnation of iridium on PtHZSM5.
The activity of Ir/PtHZSM5
was tested for npentane
isomerization under hydrogen stream. The introduction of iridium did
not change the bands observed at 3740, 3665 and 3610 cm−1 indicating that neither nonacidic
terminal
silanol groups nor acidic bridging hydroxyl groups interacted with the iridium. Additionally, the peaks
corresponding to the perturbed silanol groups at 3700 and 3520 cm−1 decreased significantly. Xray
photoelectron spectroscopy (XPS) analysis revealed that the iridium is in the form of IrO2. 27Al MAS NMR
confirmed the elimination of distorted tetrahedral aluminum. The presence of iridium slightly increased
the acidity of PtHZSM5
and its selectivity for isopentane.
Hydrogen adsorption FTIR indicated that
iridium enhanced the formation of protonic acid sites which may participate in the isomerization, and
inhibited the formation of hydroxyl groups at 3380, 3600 and 3680 cm−1 which may participate in the
enhancement of the cracking reaction.